National Instruments NI 9861 Manuale utente
OPERATING INSTRUCTIONS
NI 9861
1-Port, Low-Speed/Fault Tolerant CAN Module
NI 9861 Operating Instructions 2 ni.com
These operating instructions describe how to use the National
Instruments (NI) 9861 module. For information about installing,
configuring, and programming your system, refer to your system
documentation. The NI 9861 module requires the latest NI-XNET
software to be installed. The latest version of the NI-XNET
software is at ni.com/downloads.
Note The safety guidelines and specifications in this
document are specific to the NI 9861. The other
components in your system may not meet the same safety
ratings and specifications. Refer to the documentation for
each component in your system to determine the safety
ratings and specifications for the entire system.
Safety Guidelines
Caution Do not operate the NI 9861 in a manner not
specified in the user manual or operating instructions.
Product misuse can result in a hazard. You can
compromise the safety protection built into the product if
the product is damaged in any way. If the product is
damaged, return it to National Instruments for repair.
© National Instruments Corp. 3 NI 9861 Operating Instructions
Hot Surface This icon denotes that the component may be
hot. Touching this component may result in bodily injury.
Safety Guidelines for Hazardous Locations
The NI 9861 is suitable for use in Class I, Division 2, Groups A, B,
C, D, T4 hazardous locations; Class I, Zone 2, AEx nA IIC T4 and
Ex nA IIC T4 hazardous locations; and nonhazardous locations
only. Follow these guidelines if you are installing the NI 9861 in a
potentially explosive environment. Not following these guidelines
may result in serious injury or death.
Caution Do not disconnect I/O-side wires or connectors
unless power has been switched off or the area is known
to be nonhazardous.
Caution Do not remove modules unless power has been
switched off or the area is known to be nonhazardous.
Caution Substitution of components may impair
suitability for Class I, Division 2.
Caution For Zone 2 applications, install the
CompactRIO system in an enclosure rated to at least
IP 54 as defined by IEC 60529 and EN 60529.
NI 9861 Operating Instructions 4 ni.com
Caution For Zone 2 applications, install a protection
device between the CAN signals and the NI 9861 CAN
pins. The device must prevent the CAN Port-to-COM
voltage from exceeding 55 V if there is a transient
overvoltage condition.
Special Conditions for Safe Use in Europe
This equipment has been evaluated as Ex nA IIC T4 equipment
under DEMKO Certificate No. 07 ATEX 0626664X. Each module
is marked II 3G and is suitable for use in Zone 2 hazardous
locations.
Wiring the NI 9861
The NI 9861 has one 9-pin male D-Sub connector that provides
connections to a CAN bus. The NI 9861 has pins for CAN_H and
CAN_L, to which you connect the CAN bus signals. Connect these
signals using twisted-pair cable.
The port has two common pins (COM) that are internally
connected to the module’s isolated reference and serve as the
reference ground for CAN_H and CAN_L. You can connect the
CAN bus reference ground (sometimes referred to as CAN_V–) to
one or both COM pins. The port also has an optional shield pin,
© National Instruments Corp. 5 NI 9861 Operating Instructions
SHLD, that you can connect to a shielded CAN cable. Connecting
SHLD may improve signal integrity and EMC performance in a
noisy environment.
Caution You must use a UL listed ITE power supply
marked LPS with the NI 9861.
The NI 9861 requires an external power supply of +9 to +30 V to
operate. Supply power to the NI 9861 VSUP pin from the CAN bus.
Note Power on VSUP is required for CAN operation.
© National Instruments Corp. 7 NI 9861 Operating Instructions
CAN Bus Topology and Termination
A CAN bus consists of two or more CAN nodes cabled together.
The CAN_H and CAN_L pins of each node are connected to the
main CAN bus cable through a short connection known as a “stub.”
The pair of signal wires, CAN_H and CAN_L, constitutes a
transmission line. Every device on a low-speed/fault tolerant CAN
network requires a termination resistor for each CAN data line:
RRTH for CAN_H and RRTL for CAN_L.
Figure 1 shows a simplified diagram of a CAN bus with multiple
CAN nodes and proper termination resistor (Rt) locations.
Figure 1. CAN Bus Topology and Termination Resistor Locations
RTL CAN_L RTH CAN_H RTL CAN_L RTH CAN_H RTL CAN_L RTH CAN_H
CAN_H
CAN_L
Low-Speed/Fault-Tolerant
CAN Device
Low-Speed/Fault-Tolerant
CAN Device
Low-Speed/Fault-Tolerant
CAN Device
RtRtRtRtRtRt
NI 9861 Operating Instructions 8 ni.com
Connecting a CAN Bus to the NI 9861
You can connect the NI 9861 to any location on a CAN bus.
Figure 2 shows one example of connecting the NI 9861 directly to
one CAN node.
Figure 2. Connecting the NI 9861 to a CAN Device
Cabling Requirements for the NI 9861
This section deals with cabling specifications, termination
resistors, cable lengths, and the number of CAN nodes that can
exist in a system.
NI 9861
CAN Device
CAN
Cable
(With
Optional
Shield)
(SHLD)
CAN_H
CAN_L
Vsup
COM
(SHLD)
CAN_H
CAN_L
Vsup
COM
© National Instruments Corp. 9 NI 9861 Operating Instructions
Cable Specifications
Cables should meet the physical medium requirements specified in
ISO 11898, shown in Table 2. Belden cable (3084A) meets all
these requirements and should be suitable for most applications.
Termination Resistors
Unlike High-Speed CAN, Low-Speed/Fault Tolerant CAN
requires termination at the Low-Speed/Fault Tolerant CAN
transceiver instead of on the cable itself. Termination requires
two resistors, RTH for CAN_H and RTL for CAN_L. This
configuration allows the NXP Fault-Tolerant CAN transceiver to
detect and recover from bus faults. It is important to determine the
existing network’s overall termination, or the individual device’s
termination, before connecting it to a Low-Speed/Fault Tolerant
Table 2. Specifications for Characteristics of a CAN_H
and CAN_L Pair of Wires
Characteristic Value
Length-related resistance 90 mΩ/m nominal
Length-related capacitance: CAN_L and
ground, CAN_H and ground, CAN_L and
CAN_H
30 pF/m nominal
NI 9861 Operating Instructions 10 ni.com
port. NXP recommends an overall RTH and RTL termination of
100 to 500 Ω(each) for a properly terminated low-speed network.
Termination on the low-speed/fault-tolerant port of the NI 9861 is
set through the NI-XNET software to either 1 kΩor 5 kΩ.
Cable Lengths
ISO 11898-3 (Low-Speed/Fault Tolerant) defines data rates up to
125 kbits/s with the maximum bus length depending on the data
rate used and the busload. To provide a maximum communication
speed of 125 kbits/s, the overall network length should not exceed
40 m. However, you can increase the overall network length by
reducing the actual communication speed. Detailed cable length
recommendations are in the ISO 11898-3 specifications.
Number of CAN Nodes
The maximum number of nodes depends on the electrical
characteristics of the nodes on the network. If all of the nodes
meet the requirements of Low-Speed/Fault-Tolerant CAN, up to
32 nodes may be connected to the bus.
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